Automated data storage libraries are known for providing cost effective access to large quantities of stored data. Generally, data storage libraries include a large number of storage slots at which are stored portable data storage media. The typical portable data storage media is a tape cartridge or an optical cartridge. An accessor typically accesses the data storage media from the storage slots and delivers the accessed media to a data storage drive for reading and/or writing data on the accessed media. One or more controllers both operate the accessor to access the media and operate the data storage drives to transmit and/or receive data from an attached on-line host computer system.
In a conventional automated data storage library, the storage slots are arranged in a planar orthogonal arrangement forming a "wall" of storage slots for holding data storage media. The plane may be a flat plane, or may be a cylindrical surface. To double the storage capacity, two "walls" of storage slots may be provided on either side of the accessor.
A number of different companies manufacture automated data storage libraries today, each model displaying various different features. One example is the IBM 3494 Data Storage Library, which stores magnetic tape cartridges.
A library controller typically comprises a micro-processor, including a disk drive, and input/output adapters, such as SCSI ports. The disk drive typically stores the programs (microcode) which cause the controller to operate the library, and include information indicating the characteristics of the particular library. For example, not all libraries are identical, and the particular library may have a particular set of options. Further, the particular library may include a particular set of engineering changes. The programs for the controller may be installed or updated by a typical input device, such as a CD-ROM optical drive, but the specific instructions characterizing the specific library are typically manually entered or manually selected, and the specific instructions are typically stored on the disk drive.
The controller disk drive is subject to "crashes" or other failures requiring replacement of the disk drive. The microcode may be restored on the replacement disk drive by installing the microcode at the CD-ROM, but the specific instructions characterizing the specific library would be lost, and would have to be manually entered or manually selected. A difficulty is that there may be no record known by or available to the operator or the disk drive installer to identify the specific characterization of the library.
As taught by IBM Technical Disclosure Bulletin, Vol. 36, No. 06B, pages 545-7, P. Chang et al., "Teach Mastering Process for an Automated Tape Library", June 1993, (hereinafter, P. Chang et al. IBM TDB) an automated data storage library having a vision system calibration sensor mounted on the accessor, may use the calibration sensor to calibrate the positioning of a picker gripper relative to the calibration sensor of the accessor, and then the calibration sensor detects targets aligned with the location of the storage slots, so that the accessor may correctly access the desired data storage media from the storage slots.
In the typical automated data storage library, the accessor moves in orthogonal X and Y directions to position a picker at a desired storage slot. The picker then moves a gripper in the Z direction to grip the desired data storage medium located in the storage slot and then the picker retracts the gripper to pick the desired data storage medium from the storage slot. The accessor then transports the data storage medium to a new desired location.
This alignment between the accessor and the storage slots is required to ensure that the accessor can successfully pick data storage media from and return them to the storage slots in a reliable manner. In large automated data storage libraries, such as the IBM 3494 Data Storage Library, this alignment to each of banks of storage slots is conducted at the time of manufacture and checked again at the time of installation in the customer's facility.
After any calibration sensor and accessor misalignment is corrected (or "taught") in accordance with the P. Chang et al., IBM TDB, the alignment with respect to a target is checked, the target having been aligned with a bank or group of storage slots. For example, one target may be associated with a common grouping or bank of storage slots on one side of the accessor, and another target associated with another common grouping or bank of storage slots on the opposite side of the accessor. The accessor is typically moved to a "home" location, and the X and Y coordinates of the accessor are set to zero by the controller. Then the accessor and calibration sensor are moved to the expected location of a desired target. The calibration sensor may then scan the target to detect any misalignment between the expected location of the target and its actual location. The X and Y coordinates of the actual location of the target is stored in a table in a data base of the controller and later used to direct the accessor to retrieve a desired data storage media at a desired storage slot. This teaching process and the table are conventionally stored in the controller disk drive.
It has been found that, after calculating the misalignments, a constant misalignment, or offset, may exist in the library. Typically, this offset is in the vertical, or Y, direction, resulting in the accessor being misaligned by a small percentage of a storage slot height. Although the accessor may initially work with the small misalignment offset, the accessor may not provide consistent reliability.
This offset may be evaluated during the manufacturing process by observing whether consistent and reliable operation can be performed throughout an operating window. For example, the accessor may be moved off center by a small amount, and the accessing operation checked. The results of the observed performance can be used to compute the offset needed. The resultant offset may be manually entered into a database of the library controller, such as the above calibration table.
However, when the controller microcode is altered or upgraded, the manually entered offset may be deleted, as may the target calibration. The microcode may operate the accessor in accordance with the P. Chang et al. IBM TDB to calibrate the accessor and the target locations, but the offset required for consistent reliability may be unknown or unavailable to the operator.
Further, the controller disk drive may fail as described above, and the offset may be unknown or unavailable to either the operator or the disk drive installer when the microcode is restored.
It may be possible to adjust a master target located on a teach master bracket for the calibration sensor to correct any deviation from perfect, however this results in machines with different teach master brackets or sensors that cannot be easily replaced in the field and is an adjustment that would be costly to perform.